For degenerated, diseased or otherwise damaged spinal columns and vertebrae, it is known to treat these defects by removal of all or a portion of the vertebral disc and inserting an implant such as a spinal implant to restore normal disc height and spine orientation, and repair the spinal defects. When desired, osteogenic material also can be implanted into the intervertebral space to enhance arthrodesis, or spinal fusion between the two vertebrae adjacent to the intervertebral space. Selected implants are formed to provide a cavity for receipt of the osteogenic material.
The spinal column can exert considerable force on the individual vertebrae, and consequently also on any implant implanted in between the vertebrae. Often for defective or diseased vertebrae the bone tissue in the center of the endplate, where the vertebral body is normally only covered by a thin cortical bone layer, is weakened. The strength and integrity of the endplate may be compromised. Implants inserted in between these weakened bone tissue can subside or sink into the vertebral body. This results in a failure to maintain the desired disc space height and causes tremendous pain to the patient.
Additionally, arthrodesis or fusion of the vertebrae adjacent is recommended to treat a damaged disc or diseased vertebra. Spinal implants typically are formed of a metal such as titanium or surgical steel. While the selection of the implant configuration and composition can depend upon a variety of considerations, for arthrodesis it is often desirable to select a material that does not stress shield the bone ingrowth. Titanium and surgical steel provide the requisite strength to maintain correct disc space height and orientation; however, some evidence exists that these materials may stress shield the bone. Bone and bone derived material can provide an acceptable material having the similar strength and compressibility as living bone tissue. However, suitable donor bone is scarce. Further, extensive screening and testing must be strictly performed to minimize any risk either real or perceived for the transmission of infections from the donor to the recipient.
The following are representative of the current state of the art for the relevant technology.
A vertebral implant is described in WO-95/08306 issued to Beckers (U.S. Pat. No. 5,888,224). Intervertebral implant comprises an elongated body formed of a titanium or titanium alloy material and having a shape that is basically lens-shaped with a width less than its height and provided with or without an internal cavity. Implantation of the implant requires distraction of the adjacent vertebral bodies, insertion of the implant, which is then rotated about its longitudinal axis.
Another vertebral implant is described in U.S. Pat. No. 4,834,757 issued to Brantigan. This vertebral implant has a parallelepiped shape and comprises an outer surface completely covered with nubs or barbs that are embedded into the channel cut into the endplates.
An intervertebral implant is described in WO 96/27348 (U.S. Pat. No. 6,059,829) issued to Schlapfer et al.; the implant consists essentially of a frame about an internal cavity and includes longitudinal sidewalls having perforations therethrough. The frame is open without restriction on the top and bottom. The upper and lower surfaces are convex and join the longitudinal sidewalls and the two endwalls of the frame at sharp edges.
Another implant that is described in FR 7/10664 issued to Liu et al. This metallic implant has upper and lower surfaces that include paired projections extending vertically from these surfaces for cutting into and piercing the cortical endplate in opposing intervertebral bodies without resting on soft cancellous bone. The upper and lower surfaces also include pairs of opposed bearing surfaces to contact the uncompromised cortical bone portion of vertebral bodies.
In light of the aforementioned described problems for treating spinal defects, there is a continuing need for advancements in the relative field, including treatment of damaged or diseased spinal columns, improved implants, selection of suitable materials from which implants can be formed and methods of promoting bone fusion between the adjacent vertebrae. The present invention is such an advancement and provides a wide variety of benefits and advantages.